Bridged-gap inductor



Dec. 26, 1961 J. c. HEFFERNAN 3,014,268

BRIDGED-GAP INDUCTOR Filed April 16, 1957 Fig. I 'Q- l4 I i 3| l3] [fl Fig. 2 |3b 30 Be 3d I I I I36 a I I I INVENTOR.

JAMES C. HEFFERNAN ATTORNEYS the E-I type of core of the C type of core.

;by an internal mandrel and external presses.

United States Patent Ofiice 3,014,268 Patented Dec. 26, 1961 3,014,268 BRIDGED-GAP INDUCTOR James C. Hetfernan, Beverly, Mass., assignor, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Filed Apr. 16, 1957, Ser. No. 653,206 8 Claims. (Cl. 29-15558) through automatic punch presses to form similar laminations. The laminations are then stacked together to form the core elements. The center leg of the E-shaped core element passes through the opening in the coil formed 'by the windings and the lateral surface of the I portion is then brought into abutting relationship with the ends of the legs of the E-shaped element.

Another common type of core is the so-called C-core. Such cores are usually fabricated by winding strip metal tightly about an elliptical form in the general shape of an O. The tightly wound material is impregnated with a high temperature cement and the cement is then cured to form the strips into a substantially solid body. The body is then cut in halves to form two similar C-shaped core members. The ends of the C-shaped members are then ground and polished to provide two pairs of closely matched abutting end surfaces. These end surfaces are brought together through the opening of a coil or in some cases, through the openings of a pair of coils. In some instances, two pairs of cores are used and the coil interlinks the two cores, each of which is formed by a pair of C-cores.

There are numerous disadvantages in the use of either The cost of manufacture of inductors having such cores tends to be excessive because of the expensive fabrication equipment required. Furthermore, particularly in the case of the El type of core, the quality of the end product leaves 'something to be desired. On the other hand, in the case of the G-type cores, the cost of labor for performing the many process steps is quite high.

These disadvantages have not gone unrecognized and considerable effort has been expended in recent years to develop better and more eflicient methods of fabricating inductors. The concept of forming the cores from commercially available strips of magnetic material such as cold-rolled silicon steel, has been explored with varying degrees of success. In one technique, the magnetic material is wound in a spiral and later formed and shaped In this manner, an annular or a rectangular core element can be formed. Usually, one side of the annular or rectangular loop is cut through to permit the loop to be spread apart to interlink it with a coil of wire. In other processes using strip magnetic material, separate sides of a magnetic core are formed by riveting strips together, after which the sides are assembled to form rectangular or annular cores interlinked with a coil. Numerous modifications of these techniques have also been developed wherein air gaps between strips are staggered or strip ends are overlapped to prevent undue concentration of flux in the area of the air gap.

The common flaw of all the more recently developed techniques of fabricating inductors with cores formed of strip magnetic material is their inability to be manufactured by automatic machinery. Each of the techniques described relies to a. great extent upon manual operations, especially in the assembly of the core members about the coil. This dependence upon hand labor has effectively prevented widespread adoption of any of the processes described.

It is, therefore, a primary object of the present invention to improve the efficiency and ease of fabrication of inductors.

Another object of the invention is to provide inductors having improved cores.

Still another object of the invention is to provide a method of fabricating inductors which is easily adapted to automatic machinery and high speed production.

A further object of the present invention is to provide a relatively inexpensive method for constructing inductors of high standards of quality and performance.

In general, the invention consists in the fabrication of inductors having cores made from commercially available reels of strip magnetic material such as silicon steel.

The method is adaptable to'automatic and high-speed production from the original formation of laminations to the assembly of the core elements about the coil. First a coil is formed with as many windings as are necessary for the application to which the inductor is ultimately to be put. The coil may be generally annular in shape, or may be rectangular and provided with a rectangular central opening. A continuous length of strip magnetic material is provided, as for example, on a reel. One end of the strip is fed out from the reel, formed into a substantially closed loop, and cut from the remainder of the strip. The first portion of the strip material so cut is of a size sufficient to be linked with the coil. The loop is then spread open and one end is passed through the coil. When the loop end has passed entirely through the coil, the loop closes and is interlinked with the coil. Additional lengths of the strip magnetic material are similarly fed out, bent into loops and cut from the remainder of the strip. The additional loops are made progressively larger and each is similarly interlinked with the coil. Preferably, the loops are inserted either in groups, or one by one, alternately from opposite ends of the coil in order that the gaps between the cut ends of the loops will not form a continuous air gap through the entire core.

These and other objects and features of the invention will be more readily understood and appreciated from the following detailed description of a preferred embodiment thereof selected for purposes of illustration and shown in the accompanying drawings in which:

FIG. 1 is a view in front elevation of a transformer in substantially completed form constructed in accordance with the method of the invention,

FIG. 1a is an enlarged view, partly in section, of a portion of the transformer illustrated in FIG. 1 showing detail on the discontinuous air gap, and

FIG. 2 is a section-a1 view of an inductor in the process of fabrication.

The embodiment of the invention shown in FIG. 1 is a transformer in which the coil 12 is composed of two windings although the invention is generally applicable to inductors having any number of windings. The cores 13 and 14 are formed of nested laminations assembled upon the coil 12 in a manner that is described in detail below. Successive groups of laminations in each of the cores 13 and 14 are oriented such that the air :gap for each group is bridged by the laminations of adjacent groups. In the absence of such bridging, core losses in the inductor would be greater than is desirable. Such excessive core losses are caused by overworking of the magnetic material adjacent the air gap by the fringing of fiux. It is not essential that the bridging be done in groups of laminations as shown, inasmuch as each successive lamination could be disposed relative to neighboring laminations in such a manner that its air gap would be bridged at each side by a single adjacent lamination.

Extending downwardly from coil 12 are leads 16, 17, 18 and 19. These leads are actually the ends of a pair of windings, and electrical connection is made to those windings by means of pins 21, 22, 23 and 24. These pins pass through an insulating plate 25 which is fixed in the metallic mounting plate 26. A pair of end lugs 27 and 28 which are formed integrally with the mounting plate 26 are bent inwardly upon themselves. The lugs 27 and 28 have cars 31 and 32 extending laterally outwardly adjacent their ends. A flexible metallic strap surrounds the core elements 13 and 14 and passes under the ears 3-1 and 32. This strap is drawn tight and welded to enclose the core elements and hold them in fixed relationship to the mounting plate 26. It is usually the custom either to pot the entire transformer with the exception of the mounting plate in a resin, or to place a shielding container in the form of a metallic can over the transformer as a final step. This has been eliminated in the showing of FIG. 1 to permit easier visualization of the components and their disposition.

In FIG. 1a the air gaps between the ends of the vari ous laminations are illustrated in enlarged detail. The flexible strap which normally binds the core elements together and to the mounting lugs has been eliminated in order not to confuse the showing of the laminations. The air gaps in the outermost lamination of each of the core elements 13 and 14 appear at points slightly displaced from the center of the upper center of the transformer. The air gap in the next adjacent lamination is slightly below and displaced outwardly from the center relative to the first air gap. The air gap in the third lamination is not shown in FIG. 1a but as may be seen by references to FIG. 1 appears at the lower center portion of the transformer as does the air gap of the fourth lamination. The air gap of the fourth lamination is diagonally adjacent that of the third. Again, in the upper center area, the air gaps of the fifth and sixth laminations of both core elements appear at points diagonally displaced from the air gaps of the first pair. As is clear, the gaps in each pair of laminations are bridged by adjacent laminations. Thus, by alternately reversing the direction of insertion of the laminations either one-byone, in pairs, or in larger groups, from one end of the transformer to the other, it is possible to bridge the air gaps in the entire core structure without deforming the structure in the area of the air gap or otherwise disturbing the path of flux in a finished inductor.

The method by which the structure described is obtained may best be seen by reference to FIG. 2. After a coil 12 containing the desired number of windings has been formed, the first lamination 13a of the core element is formed. An automatic bending brake is utilized and a reel of strip magnetic material such as cold-rolled silicon steel is provided adjacent the bending brake. The strip material is fed into the brake wherein three bends are made to form the strip into a rectangular element. The rectangular element or loop is then cut by the action of a cutter combined with the brake from the remainder of the strip. The cut'ends of the loop are spread apart and the long leg of the loop adjacent the cut ends is inserted upwardly through the opening in coil 12. The material of the loop, silicon steel strip, for example, is somewhat springy and the loop reassumes the shape into which it was formed on the brake becoming the first lamination 13a.

Another length of material is fed through the brake and bent into a second loop similar to, but slightly larger than, the first loop. It is spread open and may be linked with coil 12 in the same manner as the first loop, if an end product such as illustrated in FIG. 1 is desired. The second loop becomes lamination 13b.

A third loop is similarly formed, out from the length of material and spread apart. It is of slightly larger dimensions than the second loop and the long leg adjacent the cut is inserted downwardly through the opening of coil 12. This loop reassumes its shape and becomes lamination 130. The process is repeated to provide lamination 13d.

A fifth loop, 13c, is shown in the process of being linked with the coil 12 in FIG. 2. its direction of insertion is the same as that of loops 13a and 13b. As is clear from the drawing, each pair of loops or laminations is so disposed that the air gaps of the pair are bridged by adjacent laminations. The various loops or laminations may be inserted alternately from opposite directions singly or in groups as shown in the drawing, depending upon the type of machinery available and. the application for which the inductor is designed. The process is continued until a core element having the desired number of laminations is built up on the first leg of core 12 and the entire process is repeated for the second leg of core 12, with a complete inductor is formed.

Although what has been disclosed constitutes a presently preferred embodiment of the invention, numerous variations of the process will suggest themselves to those skilled in the art. By way of example, neither the laminations of the corenor the coil itself need be in the exact shape shown, fabricating of the inductor according to the principles of the invention not being dependent upon such shapes. These and other variations are believed to be within the purview of the present invention, and accordingly, the invention should be limited only by the spirit and scope of the appended claims.

What is claimed is:

l. The method of constructing an electrical inductor which comprises forming a coil of wire with a central opening, bending a first length of constant width magnetic material into a substantially closed loop, cutting said loop from said length of material, spreading the cut ends of said loop apart, passing one of said cut ends through the opening in said coil of wire, closing said cut ends to interlink said loop with said coil of wire, bending further lengths of magnetic material into substantially closed loops, cutting said substantially closed loops from said length of material and assembling said additional progressively larger and substantially closed loops over said first loop, alternating the direction of assembling said additional substantially closed loops such that the space between the cut ends of each loop is bridged by adjacent loops.

2. The method of constructing an inductor which comprises forming a generally annular coil of wire, bending a first portion of constant width strip magnetic material three times upon itself through right angles about parallel axes to form a first generally rectangular core member, cutting said first core member at a corner thereof from said strip magnetic material, spreading the cut ends of said first core member apart, passing a long leg of said first rectangular core member in a first direction through the opening in said annular coil of wire, similarly bending and cutting a second rectangular core member from said strip magnetic material, said second member being sufiiciently larger than said first memher to fit thereover, spreading the cut ends of said second member apart, passing a long leg of said second rectangular core member in a direction opposite to said first direction through said annular coil, said second core member enclosing said first core member, and similarly bending, cutting and inserting additional core members, the direction of insertion being alternated as in the insertion of said first and second members to provide a magnetic core linked with said coil and having a discontinuous air gap at two of its corners.

3. The method of constructing an electrical inductor which comprises forming a coil of wire including at least several windings into a substantially annular body, providing a length of constant Width strip magnetic material having at least a free end, bending a first portion of said length of magnetic material into a substantially closed loop, cutting said first loop from said length of material, the free end of said material being adjacent and matching the cut end in said first loop, spreading said ends apart, interlinking said first loop with said annular body of wire by passing an end through the opening in said annular body, similarly bending, cutting, spreading and interlinking progressively larger loops of magnetic material With said annular body to form a magnetic core, alternating the direction of interlocking said loops such that the relative orientation of said loops is varied to provide air gaps between the cut ends which extend through not more than a few of said loops.

4. The method of constructing an electrical inductor Which comprises forming an annular coil of wire, bending a first portion of a continuous length of constant width strip magnetic material into a first substantially closed loop, cutting said first loop from said length of magnetic material, linking said first loop to said coil of Wire by spreading the cut ends of said loop apart, passing one of said out ends in a first direction through the opening in said annular coil and reforming said first substantially closed loop, bending a second portion of said continuous length of material into a second substantially closed loop, said second loop being slightly larger than said first loop, cutting said second loop from said length of material, linking said second loop to said coil of wire by spreading the cut ends thereof apart, passing one of said out ends in a second direction through the opening in said annular coil, said second direction being opposite to said first direction, reforming said second substantially closed loop about said first substantially closed loop, bending further lengths of said magnetic material into substantially closed loops, cutting said substantially closed loops from said continuous length of magnetic material and assembling upon said coil said additional loops of strip magnetic material, each such loop being sufiiciently larger than its preceding loop to fit closely thereabout to form a first magnetic core element, and alternating the direction of assembling said additional loops such that the air gap of each loop is bridged by adjacent loops.

5. The method defined in claim 4 wherein a second core element is formed and assembled with said coil in the same manner as said first core element to provide an inductor having two core elements with discontinuous air gaps, each of said two core elements having a leg thereof passing through the central opening in said annular coil of Wire.

6. The method of constructing an inductor which comprises forming a generally annular coil of wire, feed ing out a first length of constant width strip magnetic material, bending said first length of strip magnetic material three times upon itself and about parallel axes to form a first substantially rectangular core member, cutting said first core member at a corner thereof from said length of magnetic material, spreading the cut ends of said first core member apart, interlinking said first core member with said coil, bending, cutting, spreading and interlinking additional core members with said coil to form a first magnetic core element, each said member being sufiiciently larger than the preceding member to fit closely thereover, alternating the direction of interlinking said members such that said members are oriented relative to one another and to said coil as to form discontinuous air gaps at two of the corners of said magnetic core element.

7. The method defined in claim 6 wherein a second core element is formed and assembled upon said coil in the same manner as said first core element, the air gaps at the two corners of said second core element being adjacent the air gaps at the two corners of said first core element.

8. The method defined in claim 7 including peripherally binding said first and said second core elements together and mounting said bound elements and said coil upon a base to form an inductor.

References Cited in the file of this patent UNITED STATES PATENTS 1,429,814 Weiss Sept. 19, 1922 1,935,426 Acly Nov. 14, 1933 2,408,211 Hodnette Sept. 24, 1946 2,456,941 Hodnette Dec. 21, 1948 2,523,071 Sommerville Sept. 19, 1950 2,548,624 Sclater Apr. 10, 1951 2,586,532 Grandfield Feb. 19, 1952 2,655,717 Dunn Oct. 20, 1953 2,683,474 Langenberg July 13, 1954 2,700,207 Zimsky Jan. 25, 1955 2,869,591 Larkin Jan. 30, 1959 FOREIGN PATENTS 106,986 Great Britain June 14, 1917 

